Impact of the Respiratory Motion and Longitudinal Profile on Helical Tomotherapy

So Hyun Park; Jinhyun Choi; JinSung Kim; Sohyun Ahn; Min Joo Kim; Ho Lee; Seo Hee Choi; Kwangwoo Park

doi:10.14316/pmp.2018.29.1.1

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Park, Choi, Kim, Ahn, Kim, Lee, Choi, and Park: Impact of the Respiratory Motion and Longitudinal Profile on Helical Tomotherapy

Original Article

Progress in Medical Physics 2018;29(1):1-7.

Published online: 20 March 2018

DOI: https://doi.org/10.14316/pmp.2018.29.1.1

Impact of the Respiratory Motion and Longitudinal Profile on Helical Tomotherapy

So Hyun Park^∗, Jinhyun Choi^∗, JinSung Kim^†, Sohyun Ahn^†, Min Joo Kim^†, Ho Lee^†, Seo Hee Choi^†, Kwangwoo Park^†

^∗Department of Radiation Oncology, Jeju National University Hospital, Jeju University College of Medicine, Jeju, Korea

^†Department of Radiation Oncology, Yonsei Cancer Center, Yonsei University College of Medicine, Seoul, Korea

Corresponding author Kwangwoo Park (KPARK02@yuhs.ac) Tel: 82-2-2258-4362 Fax: 82-2-2227-7823

This is an Open Access article distributed under the terms of the Creative Commons Attribution Non-Commercial License (http://creativecommons.org/licenses/by-nc/3.0) which permits unrestricted non-commercial use, distribution, and reproduction in any medium, provided the original work is properly cited.

Abstract

The TomoTherapy^® beam-delivery method creates helical beam-junctioning patterns in the dose distribution within the target. In addition, the dose discrepancy results in the particular region where the resonance by pattern of dose delivery occurs owing to the change in the position and shape of internal organs with a patient's respiration during long treatment times. In this study, we evaluated the dose pattern of the longitudinal profile with the change in respiration. The superior-inferior motion signal of the programmable respiratory motion phantom was obtained using AbChes as a four-dimensional computed tomography (4DCT) original moving signal. We delineated virtual targets in the phantom and planned to deliver the prescription dose of 300 cGy using field widths of 1.0 cm, 2.5 cm, and 5.0 cm. An original moving signal was fitted to reflecting the beam delivery time of the TomoTherapy^®. The EBT3 film was inserted into the phantom movement cassette, and static, without the movement and with the original movement, was measured with signal changes of 2.0 s, 4.0 s, and 5.0 s periods, and 2.0 mm and 4.0 mm amplitudes. It was found that a dose fluctuation within ±4.0% occurred in all longitudinal profiles. Compared with the original movement, the region of the gamma index above 1 partially appeared within the target and the border of the target when the period and amplitude were changed. Gamma passing rates were 95.00% or more. However, cases for a 5.0 s period and 4.0 mm amplitude at a field width of 2.5 cm and for 2.0 s and 5.0 s periods at a field width of 5.0 cm have gamma passing rates of 92.73%, 90.31%, 90.31%, and 93.60%. TomoTherapy^® shows a small difference in dose distribution according to the changes of period and amplitude of respiration. Therefore, to treat a variable respiratory motion region, a margin reflecting the degree of change of respiration signal is required.

Keywords: TomoTherapy^®, 4D CT, Moving phantom, Period, Amplitude

References

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Fig. 1.

The setup of QUSAR phantom and Abches system for acquiring the motion signal.

Fig. 2.

(a) Target 1 and Target 2 of 3.0 cm diameter and 6.0 cm length in a QUASAR^TM phantom film cassette and Organs at Risk (OARs); (b) EBT3 film inserted in film cassette.

Fig. 3.

The longitudinal profile according to change of phase and amplitude at the center axis (a) 1.0 cm field width; (b) 2.5 cm field width; (c) 5.0 cm field width.

Fig. 4.

The longitudinal profile according to change of phase and amplitude at the region shifted left 1.5 cm from center axis (a) 1.0 cm field width; (b) 2.5 cm field width; (c) 5.0 cm field width.

Fig. 5.

The longitudinal profile according to change of phase and amplitude at the region shifted right 1.5 cm from center axis (a) 1.0 cm field width; (b) 2.5 cm field width; (c) 5.0 cm field width.

Fig. 6.

2D gamma index map (a) 5.0 s period, 1.0 cm field width; (b) 4.0 mm period, 1.0 cm field width; (c) 5.0 s period, 2.5 cm field width; (d) 4.0 mm period, 2.5 cm field width; (e) 5.0 s period, 5.0 cm field width; (f) 4.0 mm period, 5.0 cm field width; Red (dark): Gamma index >1.

Table 1.

Gamma passing rates within the target for each period and amplitude according to field width compared with origina movement.

	Field width
	1.0 cm	2.5 cm	5.0 cm
2.0 s Period	95.50%	97.87%	90.31%
4.0 s Period	97.79%	96.11%	97.08%
5.0 s Period	95.52%	92.73%	93.60%
2.0 mm Amplitude	97.92%	97.10%	98.71%
4.0 mm Amplitude	96.15%	90.31%	95.21%

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